Ultra-low k (ULK) dielectric materials possess many properties desired in semiconductors. For instance, a layer, or film, of ultra-low k dielectric material may contain pores within the layer that help to reduce the capacitance of the semiconductor. However, the presence of these pores also necessarily decreases the strength of the film, resulting in a decrease in the film's stability during the semiconductor patterning process. The more pores present in the film, the greater the resulting damage to the ultra-low k dielectric material during processing.
Existing techniques for strengthening the ultra-low k layer include stuffing the pores in the layer with a substance during the subsequent processing steps. Frot et al. (Adv. Mater. 2011, 23, 2828-2832) describe filling the pores of an ultra-low k layer with an organic polymer, then subsequently removing the organic polymer, to mitigate the effects of patterning and other downstream processing steps. A pore-stuffed ultra-low k layer can be used for protection of the ultra-low k layer from reactive ion etching and for the prevention of precursor penetration in subsequent chemical vapor deposition (CVD) or atomic layer deposition (ALD) liner processes. The strengthened layer also could provide more process margin during the chemical-mechanical planarization (CMP) process.
Substances such as manganese react with dielectrics, such as those found in an ultra-low k film, to form a self-forming barrier (SFB). This integration of the self-forming barrier and the dielectric material is important for RC reduction. However, when the pores are stuffed, as described above, there are concerns about the integration of the self-forming barrier with the pore-stuffing material in the ultra-low k layer, rather than with the dielectric material. A reaction between the pore-stuffed material (that is, due to unexposed dielectric layer in the trench or via) and the self-forming barrier could lead to contamination of the self-forming barrier, resulting in the potential for the formation of a discontinuous self-forming barrier layer. Accordingly, a method is needed to provide for a continuous dielectric layer in a pore-stuffed ultra-low k layer.